Returns the io_service
object through which the async_write_some
handler h will
be invoked.

a.async_write_some(cb,h);

void

Initiates an asynchronous operation to write one or more bytes
of data to the stream a.
The operation is performed via the io_service
object a.io_service()
and behaves according to asynchronous
operation requirements.

The constant buffer
sequence cb specifies
memory where the data to be written is located. The async_write_some operation shall
always write a buffer in the sequence completely before proceeding
to the next.

The implementation shall maintain one
or more copies of cb
until such time as the write operation no longer requires access
to the memory specified by the buffers in the sequence. The program
must ensure the memory is valid until:

— the last copy
of cb is destroyed,
or

— the handler for the asynchronous write operation
is invoked,

whichever comes first.

If
the total size of all buffers in the sequence cb
is 0, the asynchronous
write operation shall complete immediately and pass 0 as the argument to the handler
that specifies the number of bytes written.